This invention relates to bioderived plasticizers for use with biopolymers. As used herein the term “bioderived” means made from plant-made molecules that are either directly expressed from plants, such as sugars, starches or fats, or fermented from plant-made molecules, such as sugars, starches, or fats. As used herein the term “biopolymers” means polymers made from plant derived molecules.
The disclosed bioderived plasticizers act as modifiers that change the flexural properties and thermomechanical properties, such as the heat deflection temperature, of biopolymers while maintaining miscibility between the plasticizer additive and the parent biopolymer. As used herein the term plasticizer means a molecule that improves physical, mechanical or thermal properties of a polymer. In one embodiment the modifier acts as a plasticizer to improve the flexibility of the biopolymers without adversely affecting the Young's Modulus or bleeding out at high temperature or over time, such as in storage. In another embodiment the plasticizer acts to improve the heat deflection temperature of PLA.Polylactic acid (PLA) is becoming a widely used biopolymer due to its biocompatibility, biodegradability and sustainability. Polylactic acid is expected to expand its application base because (1) the raw material L-lactic acid can be inexpensively produced in a large scale by a fermentation process, (2) degradation velocity of polylactic acid is high in the compost, and (3) polylactic acid is excellent in its resistance to fungus and its ability to protect foods from odor or color contamination. Preparation of high molecular weight lactic acid polymers can be conducted by (1) ring-opening polymerization (ROP) of the dehydrated ring-formed dimer or dilactide, (2) polycondensation and manipulation of the equilibrium between lactic acid and the polylactide by removal of the reaction water using drying agents, or (3) polycondensation and linking of lactic acid prepolymers. Polylactic acid has the following general formula:

Polylactic acid is generally brittle and exhibits a low softening temperature, thus making it unsuitable for applications that require flexibility, toughness, or heat resistance such as agricultural multi-films, food packaging bags, garbage bags, hot-filled cups, microwaveable bowls and other polymeric films, foams and rigid durables. Improved rigidity improves suitability for such things as computer casings, automotive parts and secure packaging.
Generally known techniques for making polylactic acid flexible are (1) copolymerization, (2) addition of a plasticizer, and (3) blending of flexible polymers. Though these techniques generally improve the flexibility of the polylactic acid, there are problems associated with their use. Technique (1), immediately above, creates a material that generally has the properties needed for flexible films, but the production usually requires a large layout of capital which limits its use to large manufacturers of base resin. Technique (2) is used to “soften” a range of polyesters including polylactic acid or polyhydroxybutyrates (PHB), but the plasticizers tend to bleed out over time. Another issue is that techniques (1) and (2) lower the glass transition temperature of the resin composition but this also changes the physical properties such as making the material less strong as seen in a lowering of the tensile modulus.
Technique (3) above usually involves blending two polymers with desired properties such as blending a flexible non-bioderived resin with a bioderived, biodegradable resin. Examples include blends with polybutylene terephthalate-adipic acid, polybutylene succinate, polyethylene succinate, polycaprolactone with D-polylactic acid and L-polylactic acid. In some cases, additional plasticizers such as citrus esters are still used in addition to the polymeric plasticizers (U.S. Pat. No. 7,166,654). Examples of these resins have been disclosed in BASF U.S. Pat. Nos. 5,817,721, 5,889,135, and 6,018,004, Eastman Chemical U.S. Pat. Nos. 6,342,304, 6,592,913, and 6,441,126, and Japanese Patent HEI 8-245866 and HEI 9-111107, which are incorporated herein by reference.
Linear polyesters of diols and diacids have been used as plasticizers for polymers from PVC to highly crystalline polyesters of polycarbonate, polylactic acid, and other polyhydroxyalkanoates. Several of these materials have been made commercially available including BASF Ecoflex, Eastman Chemical's EastStar Bio, and Showa High Polymer Company's Bionolle U.S. Pat. No. 5,324,794. Blends made with these materials tend to have reduced modulus and they are not optically clear.
It would be an advancement in the art to provide a polymeric plasticizer that improves the flexibility of the biodegradable polymer without adversely affecting the Young's Modulus.
It would be a further advancement in the art to provide a plasticizing agent that can be blended into biodegradable polymers as well as petrochemically derived polyolefins to produce products, such as films used for garbage bags, packaging materials, injection molded parts, bottles and the like, that have excellent toughness and flexibility at low plasticizer concentrations without sacrificing physical properties such as the Young's Modulus.
It would be yet another advancement in the art to provide a polymeric plasticizer that may be blended with PLA, other polyesters such as PHAs, HIPS, ABS, polystyrene, or polyolefins such as polyethylenes, polypropylene, or copolymers of the polyethylene that shows improved compatibility and outstanding resistance to bleeding out at high temperature or over time.
It would be still another advancement in the art to provide a polymeric plasticizer that has been grafted to the backbone of polyolefins using an unsaturation functionality of the copolymer plasticizer so that the plasticizer is readily miscible with a wide range of polymers.
It would be a further advancement in the art to provide a polymeric plasticizer that can be used as a compatibilizer or an emulsifier for polyolefin/polyester blends and/or polyolefin/starch blends.
Generally known techniques for making polylactic acid more temperature tolerant are (1) induced crystallization, (2) copolymerizing with polymers with higher glass transition temperatures, and (3) blending polymer enantiomers to form stereocomplex structures with higher temperature stability. Enantiomers are molecules with identical chemical structure but different orientation around their optical centers; that is, they are non-superimposable mirror images of each other. In a preferred embodiment, technique (3) involves adding the enantiomers of 1 and d-PLA in a range of molar concentrations to improve temperature stability.
It would be an advancement in the art to provide a polymeric additive that can be used both as a compatibilizer for blends of different enantiomers of the same polymer such as the two stereospecific forms of polylactic acid, D-PLA and L-PLA and also act as modifier to improve the heat deflection temperature of PLA such that no additional steps would be needed for post production annealing